What is the difference between RPM mode and Pressure mode on a tanker?

This mat be the same as volume pumping compared to pressure. When pumping you are going to supply a target (hose line, another rig) with a certain amount of water without worrying so much about the pressure at which it is supplied. In pressure mode you are more concerned with just that, the pressure, you want the target to receive.

For tanker ops I would work in volume mode when supplying another rig.

I am sorry I don't have a way to make this more clear. I don't have my driver operator guide nest to me to give a better answer.

It doesn't have anything to do with volume vs pressure, that's a completely different concept dealing with the operation of a dual-stage pump and how the intake of water is routed through the impellers to the discharge side of the pump (either series or parallel).

What he is asking about is the automatic pressure governor that most new apparatus have, not just "tankers". It also serves as the pressure relief valve on most applications.

Basically, it works like this:

RPM Mode (Throttle Control): The increase/decrease switch only adjusts engine speed up or down, just like a mechanical throttle would do. There are no automatic adjustments made by the apparatus, and unless you have a separate pressure relief valve on the rig, you are operating without one in RPM mode.

PSI Mode (Pressure Control): The increase/decrease switch is adjusting the engine speed based on the outgoing pressure. In this mode, once you get the pump to the desired PSI, the apparatus will monitor it and make automatic adjustments as needed. This may mean that if you open another discharge, the truck will increase engine speed to compensate for the additional required water, or if you shut down a discharge the apparatus will decrease engine speed. In this mode, the pressure relief valve is automatically set at the same pressure.

Pump in "pressure" mode. That is the main point. With most set-ups, is the only way that your pump governor is going to work properly.

Remember our goal is to pump to a specific GPM. We use pressue calculations in an attempt to get those GPMs. When you pump in RPM mode fluctuations with intake and out-take pressure will increase or decrease your PDP. If you are in Pressure mode, the pump governor will automatically account for pressure changes and react accordingly (keeping your PDP where it needs to be).

If you still don't understand... you really shouldn't be operating your tender.

If you still don't understand... you really shouldn't be operating your tender.

Just make sure when you get back from training to explain why you're asking if you trained on similar but different equipment.
The pumper I learned on at a state run fire school was of the type that once you put the truck tranny in gear and engaged the PTO,you then took the truck trnsmission lever and put it in "Neutral".
I asked about that on my return because we also ran a 1982 Ford chassis Pierce pumper.The engineer looked at me like I was nuts and explained that on ours "One does not take the truck out of gear when the pump is needed unless you want to stop the water flow,do you get me young Padawan Learner?".
The next year,he took the same course for requalification and ran into e during the lunch break and said he'd seen what I was talking about.
The thing is ,different rigs have different manual of arms so to speak,that must be understood if you're pressed into service on a fireground.

It doesn't have anything to do with volume vs pressure, that's a completely different concept dealing with the operation of a dual-stage pump and how the intake of water is routed through the impellers to the discharge side of the pump (either series or parallel).

What he is asking about is the automatic pressure governor that most new apparatus have, not just "tankers". It also serves as the pressure relief valve on most applications.

Basically, it works like this:

RPM Mode (Throttle Control): The increase/decrease switch only adjusts engine speed up or down, just like a mechanical throttle would do. There are no automatic adjustments made by the apparatus, and unless you have a separate pressure relief valve on the rig, you are operating without one in RPM mode.

PSI Mode (Pressure Control): The increase/decrease switch is adjusting the engine speed based on the outgoing pressure. In this mode, once you get the pump to the desired PSI, the apparatus will monitor it and make automatic adjustments as needed. This may mean that if you open another discharge, the truck will increase engine speed to compensate for the additional required water, or if you shut down a discharge the apparatus will decrease engine speed. In this mode, the pressure relief valve is automatically set at the same pressure.

Listen to this fella, he knows what he is talking about. It doesn't have anything to do with Pressure vs. Volume mode. It's all about pressure regulation..... which is done either by automatically adjusting the pressure (compensating) or the R.P.M. of the motor/pump (slow they R.P.M.s as they begin to rise).

For any additional questions, you should reference your manual for the pump and the manual for the pressure relief device.

That didn't come out right. What I meant to express was that by switching to PSI/Pressure Mode, it takes the PLACE of a discharge pressure relief valve. If you pump in RPM/Throttle Mode, it's no different than taking an older style pumper and pumping without turning on or setting the relief valve.

That being said, I actually HAVE seen a few trucks with both. It's not very common, but one dept I know of that spec'd their pumper with both an electronic governor AND manual discharge relief valve did it for a few reasons:

1. As a backup to the automatic governor, should the truck for some reason not compensate for an overpressure situation and lower the idle

2. The manual relief valve can still be operated when the automatic governor is in RPM/Throttle Mode

3. If you are pumping at near-idle in PSI/Pressure Mode at 80 PSI with 80 PSI incoming, and you have your intake relief valve set at 200 PSI, and all of a sudden the incoming water supply surges to 180 PSI, there is very little the automatic governor can do (since the truck is already at or near idle speed). With a manual relief valve set at 100 PSI, however, it will ensure none of that excess pressure makes its way into the hoses

No Joke......

This is no joke, I worked at an Airport that when the pumps would kick-on our hydrant pressure was around 210 p.s.i.

Needless to say, all of our vehicles with pumps that connected to the system all have Intake Pressure Relief Valves. All of our Steamer Port Intakes have the adjustable Intake P.R. Valves. Most manufactures build them into the valves I believe.

I was just asking this question.....

We have a pumper/tanker with the RPM and Pressure pump settings, and I not being the engineer, asked what the difference was between this and the Pressure/Volume setting on other apparatus. I was told it was the same as the Pressure/Volume settings for the 2 stages of the pump.

"But Captain, it's a single stage pump......" ( Blank stare as he reads the pump plate that says "Single" in the stage slot.

We have no literature on this pump, even though it is only a couple of years old, and the manufacure has been slow in getting it after my request. ( I run the maintenance program, I want details on what I'm putting a wrench to )

Thanks for the clarification folks. It makes sense now that it has been explained.

You're welcome, glad to help clear things up. It's a common misconception that it has something to do with the pressure/volume settings of a 2 stage pump, but as you can see it's something completely different!

From the Class One Manual

For every new delivery I do I take the basics from the Class One Manual and put it into a hand out for all the members of the department. What I have pasted here is just the basics and highlights I put in the handouts. Also there is a lot if info on the Class One website and CD's they hand out at shows. They have instructional vidios you can play on your computer, downloadable from their site.

MODES OF OPERATION

POWER ON - When the unit is first powered up, the display will show [MODE] and the engine will remain at idle until the mode switch is pressed to select the desired operating mode, PRESSURE or RPM. If the pump is engaged and the OK to Pump LED is illuminated, PRESSURE will be the first mode selected otherwise Throttle will be the first mode.

RPM MODE - When the unit is in RPM mode, the display will read “THROTTLE” and the green RPM LED will be illuminated. Engine speed is controlled by the INCrease and DECrease switches and the display will indicate “INCREASE” or “DECREASE” as appropriate when these switches are depressed. The governor will maintain the last output signal attained with these switches. The engine will maintain an RPM appropriate for the throttle signal being sent.

Note: if while operating in rpm mode the pressure increases more than 50 psi from the pressure logged at the last switch press, the governor will limit the pressure increase to no more than a 50 psi differential. The governor may reduce engine rpm to achieve this and the message psi limit will be displayed in the message center. Note: the governor will not attempt to regulate pressure in this mode, only limit the differential pressure to 50 psi from the pressure present when the last switch was pressed.

PRESSURE MODE - When the unit is operating in the Pressure mode, the display will show “PRESSURE” and the PRESSURE LED will be illuminated. Pump pressure is set by using the INCrease and DECrease switches. The governor will attempt to maintain the last pressure achieved with these switches. The display will indicate “INCREASE” or “DECREASE” as appropriate. The governor maintains pump pressure by controlling engine RPM in response to a signal from the pressure transducer mounted on the pump. When controlling in this manner, the display will show CTRL DEC or CTRL INC. Switching between modes by pressing the mode switch will change the governor from RPM to Pressure mode without a significant change in engine speed or pump pressure. The message center will indicate “PRESSURE” or “THROTTLE” as appropriate once the mode change has been made. When switching to PRESSURE, the pressure set point is whatever pressure is on the transducer at the change.

PRESET MODE - Pressing the PRESET switch in either mode will control the engine to attain the preset RPM or pump pressure programmed in governor memory. If there is more than 10 PSI pressure on the pump, the RPM Preset is disabled. If the Preset Switch is pressed, DISABLED will be displayed momentarily.

HIGH IDLE MODE - An input is available to bring the engine speed to a PRESET RPM (High Idle) from a remotely mounted switch. While operating in this mode, the display will show “HIGHIDLE”. This function is inoperative when the pump engaged input is active, there is more than 10 PSI on the pressure transducer or if the MODE switch on the governor has been pressed. Pressing the IDLE switch causes the high idle to drop out and the high idle input must be toggled off and then on again to reinstate high idle. The INC and DEC switches are active in high idle mode and the engine speed can be adjusted, changing engine speed in this manner will not change the preset RPM that is set in memory.

IDLE MODE - Pressing the IDLE switch at any time returns the engine to idle speed.
NOTE: A FIRM, POSITIVE SWITCH DEPRESSION IS NECESSARY TO ACTIVATE THIS FEATURE AND A QUICK PRESS MIGHT BE IGNORED.

CAUTION SENSOR - Whenever the transducer signal is below 0.3 VDC or above 4.8 VDC, a sensor fault will be logged and SENSOR will be displayed in the message center. (SENSOR will flash if the failure occurs while operating in PSI Mode) Once a failure is detected, the governor can no longer maintain a pressure setting. It will hold the current engine RPM and only operate as a throttle. Once the SENSOR message is displayed, it will not clear until power to the governor is reset. It is extremely important that the cause for this message is investigated. The governor cannot control discharge pressure properly unless the sensor signal is reliable and correct.

SWITCH SESSION PRESSURE - If the INC switch is held the governor will not allow a change greater than 80 PSI without releasing the INC switch and pressing it again. This is only applicable when the pressure is above 90 PSI. This prevents high pressures from being introduced by a distracted operator.

PRESSURE / WATER LOSS - If the discharge pressure drops below 30 PSI for any reason, engine speed will not be increased. The governor output voltage will reduce to the last known value (engine RPM) where the pressure set point was obtained. The display will flash -INTAKE- during this low pressure condition. If the pressure increases above 30 PSI, OPERATOR will flash and the governor will not increase output unless the operator presses the INC or PRESET switches. If pressure above 30 PSI is not regained within 5 seconds, the governor will return the engine to idle and display LoSupply. The operator must make certain that the water supply is adequate and then reinstate governing using the MODE, INC and/or PRESET switches.

PRESSURE RECOVERY / CAVITATION (TRIM) - The governor has a trim adjustment, this can be set between 5% and 20% of maximum throttle. This parameter limits the governor’s maximum increase in a pressure recovery attempt. The message center will flash OPERATOR when this limit is reached and the RPM will not increase further. The operator must take positive action to restore discharge pressure. If pressure is not restored within 4 seconds, the governor will reduce output to the last known output where pressure was maintained. The operator must input a new set point with the INC/DEC or PRESET switches. If the pressure rises above the original set point and the governor decreases the engine speed, the governor will resume normal governing operations.

PSI ENABLE - The pressure governor will not control pressure until a discharge pressure of 70 PSI is attained. It will act as a throttle until this pressure point is achieved.

RPM PRESET DISABLE - If there is pressure on the pump transducer, RPM Preset is disabled and a DISABLED message will be displayed in the Message Center if you try to use the preset button in the RPM Mode.

PRESSURE PRESET - While the governor is attempting to reach the preset PSI, the increase is tested at intervals and if the pressure is not increasing, the governor will maintain the engine speed at the point the pressure stops increasing and uses that as the pressure set point.

HIGH IDLE - The High Idle feature is disabled if there is less than 10 PSI at the pump transducer.

SWITCH SESSION PRESSURE – If the INC switch is held and the operating pressure is above 90 PSI, the governor will not allow a change greater than 80 PSI without releasing the INC switch and pressing it again. This is to prevent high pressures from being introduced by a distracted operator.

MESSAGES – OPERATOR will flash anytime the governor can’t achieve a desired pressure.
This indicates that the governor will not increase engine speed until the pump operator intervenes.
INTAKE- will be displayed anytime the governor is operating in pressure mode and the discharge
pressure drops below 30 PSI. If pressure remains below 30 PSI, the display will change to LoSupply and engine speed will be reduced to idle. At this point, the operator must correct the supply or discharge problem and reinstate governing OPERATOR will be displayed anytime the governor can’t achieve a function or pressure. This indicates that the governor will not increase engine speed until the pump operator intervenes. CTRL INC will be flash in the display if the governor cannot regain the set pressure. It will change to OPERATOR (flashing) if pressure cannot be regained within 4 seconds. During these periods, the governor will not command an increase in engine speed and will return to the last known engine speed command where the set point was achieved.

PUMPING OPERATION EXAMPLES

OPERATION 1 - Tank Supply for pre-connects or small diameter hose.

Upon arrival at the scene, position the apparatus and shift into pump gear using department SOP. At the pump panel, the three interlock LED’s must be ON. and the governor Message Center should display [MODE]. If the Throttle Ready Interlock is not present, NO INTLK will be displayed in the message center when the MODE switch is pressed and the governor will not respond to an increase or decrease request. The governor will check for a valid pressure transducer signal at power up, if none is found, SENSOR will be displayed. If this is the case, the governor will operate as a throttle only. It cannot react to pressure changes. The MODE switch must be depressed to select a governing mode.

Ensure that water is available to the pump by checking the Master Discharge Gauge for pressure. Prime the pump and establish water prior to pressing the governor Preset Switch. Once pressure mode is selected, the PRESET switch may be depressed to quickly bring the pump up to the preset operating pressure. The governor will respond to increase and decrease commands from the INC and DEC switches within the operating capabilities of the engine. When the INCrease switch is pressed, INCREASE is displayed in the message center. When the DECrease switch is pressed, DECREASE is displayed. Whenever the governor adjusts the engine speed to maintain the established RPM, CTRL INC or CTRL DEC will be displayed while the governor is actively adjusting engine speed to maintain the set point.

The message center will display: THROTTLE or PRESSURE to indicate the current operating mode. Whenever operating with a limited water supply, always be aware of the possibility of running out of water. When the governor is operating in pressure mode it will attempt to recover from a discharge pressure loss and increase engine RPM to compensate. If water is introduced to the pump while the engine RPM is advanced, a pressure spike will result. The magnitude will be a factor of pump speed and water quantity. It is not uncommon to lose water and regain it during operation with extremely low water levels due to the position and configuration of the tank sump.

OPERATION 2 - Transferring from tank to pressurized water source.

The transition from tank to hydrant or relay is an operation that needs to be approached with
awareness. Resultant pressure with no change in pump speed is a combination of the operating
pressure prior to the change plus the incoming pressurized supply. If operating at 125 PSI and
adding a 100 PSI pressurized water source, the resultant discharge pressure will be 225 PSI.
The governor will compensate, but it will not be instantaneous. Any time the pump receives air or
an air-water mixture, the discharge pressure will drop and the governor operating in pressure
mode will increase pump speed to maintain the set pressure. Every effort should be made to
purge or bleed air from the system. When pressurized water hits the impeller, a significant pressure
spike can occur. This may be an occasion to change the governor to RPM MODE before the
changeover, establish an adequate supply and then switch back to pressure mode. In some
instances, a decrease in RPM would be in order and then the PRESET switch can be used after
switching back to pressure mode to re-establish pressure governing.

OPERATION 3 - Transferring from tank to draft

The transition from tank to draft is another scenario that requires a knowledgeable operator/
engineer. A positive water supply must be established prior to changing the water source. If this
is not accomplished, the governor will increase pump speed and when the supply is established,
the pressure will be more than desired. If the engine RPM increases dramatically, press IDLE,
establish the water supply, press MODE and then PRESET to return to pressure governed
operation. The total time should be less than 3 seconds.

OPERATION 4 - Portable Tank (Pond)

The transition from onboard tank to portable tank is a tank to draft operation. When the portable
tank is refilled is a time when the pump operator must control the situation. When the tank gets
low, air can be introduced into the system. The operator must control this so that a pressure
spike is not introduced. When the tank is refilled from a dump, a wave action can be set up that
would allow running away from water for a short period of time. This can be controlled by switching to RPM mode temporarily while the tank is refilled.

Regarding using RPM mode for drafting, Yes do do have to start a draft operation in the RPM mode. The reason for this is that you have to show pressure on the pump of at least 30 pounds before the govener will let you increase the pressure while in the pressure mode. If you have no water in the pump you cant have the 30 pounds pressure needed so will not be able to increase the throttle. Set the controller to RPM, pull your prime, show pressure on the gauges, then switch mode to "pressure'.

easy way is this:
thinking of it like banging some chic (fat chic in my case)
rpm or revolutions per minute is how many times you hump her in one minute
psi is the pressure, or force, you use.
so do you want to hump her 40 times, aka 40 rpm, or try and break her pelvis, aka lots of pressure